The role of SETD3 in the immune system

Histone lysine methyltransferases are important in regulating gene expression, by methylating lysine residues on histones. In recent years, research has shown that many histone lysine methyltransferases are located in the cytoplasm to perform separate functions. The SET-domain containing protein 3 (Setd3) could be one of such proteins, since our initial study show a predominant cytoplasmic localization of Setd3-GFP fusion in BOSC23 cells and subsequent analysis further revealed that Setd3 is highly expressed in the cytoplasm of macrophages, T cells, B cells and dendritic cells. Moreover, we have identified that cytoplasmic Setd3 protein levels increased rapidly in macrophages upon Toll-like Receptor (TLR) activation, which is likely due to inhibition of GSK3-mediated degradation. To further study the functional role of Setd3 in various immune cells, we generated a conditional knockout mice by crossing Setd3f/f mice with Mx1¬-Cre mice to delete Setd3 in hematopoietic lineage cells1. We were able to delete Setd3 efficiently in the bone marrow and generate Setd3-deficient bone marrow derived macrophages (BMDMs). Setd3-deficient BMDMs were able to respond to TLR stimulations, as there were no differences in downstream signaling pathways. Like the wild-type BMDM, Setd3-deficient BMDMs were able to polarize into M1/M2 phenotypes, phagocytose and produce mitochondrial ROS. To study the role of Setd3 in macrophages in vivo, we generated Setd3f/fLysM-Cre mice to delete Setd3 in myeloid lineage cells. We observed reduced populations of large peritoneal macrophages (LPMs) and neutrophils in the peritoneal cavity. The small peritoneal macrophages (SPMs) were not affected, suggesting that Setd3 could be important in the localization, development or maintenance of LPMs only. Other macrophage populations in the mice are yet to be characterized. In addition, Setd3f/fMx1-Cre mice also showed normal T cell and B cell development, but with slight inhibition of B cell maturation in the spleen. As the deletion of Setd3 in peripheral T and B cells were inefficient in Setd3f/fMx1-Cre mice, we generated chimeras that were reconstituted with either Setd3f/f or Setd3-deficient bone marrow cells. We observed an obvious inhibition of B cell maturation as T2 and T3 populations were much lower in chimeric mice reconstituted with Setd3-deficient than control (Setd3f/f) bone marrow cells. The numbers of regulatory (Treg) and CD8+ T cell populations were also reduced in the spleen of these mice, hinting that Setd3 could be important in regulating B cell maturation and specific T cell populations. Since Setd3 is expressed in many immune cells, more experiments need to be done to understand the role and mechanism in which Setd3 regulates various immune cells.Master of Scienc